The invention relates to a quick disconnectable screw device. The present invention relates more particularly to a screw device with a screw piece, a first threaded part and a second threaded part, the thread of which fits with the first threaded part, wherein the screw piece has a straight guide for the first threaded part, an axial and radial bearing for the second threaded part, and the pushing direction of the straight guide and the axis of rotation of the radial bearing being arranged parallel to one another.
Screw devices of this type are generally known also as screw gears and allow a uniform conversion of movement between rotation and longitudinal. The screw joint is thus normally formed from a screw and a nut with an external and an internal thread. The distance and speed of displacement of the nut relative to the screw are selectable within wide limits by means of the screw length and the pitch of the thread as well as the rotational speed between the screw and nut. Screw gears are used, for example as setting gears in optical instruments, as a spindle displacement for tools or workpieces on machine tools and as an adjusting device or clamping device. At the same time, there is often a need to cover large displacement distances quickly, but then to make a very fine setting within a narrow range or then to exert high forces in the direction of displacement. However, since, in a screw gear, only the rotational speed is variable during operation, compromises are necessary. The situation is different if there is a possibility of cancelling the engagement of the two threads.
From S. Hildebrand, Feinmechanische Bauelemente [Precision Components], Berlin 1968, page 258 ff., a slip-on nut is known which, in addition to the threaded bore, also has a passage bore arranged obliquely relative to this. In the oblique position, the slip-on nut can be displaced freely on a screw, and after tilting in the axial direction the nut thread engages into the screw thread and normal screwing is possible with an unlimited travel. The necessary additional tilting movement is a disadvantage, at least where modifications, for example as a clamping means, are concerned.
Bayonet fastenings with a safeguard by means of a screw connection are known from Richter, v. Voss, Bauelemente der Feinmechanik [Precision Components], 2nd edition, Berlin 1938, page 160 ff. Here, two parts to be connected have an external and an internal thread which, on both parts, is milled away at three locations on the circumference, so that the parts can be plugged together and connected as a result of a rotation of approximately 60.degree. . Quick-acting clamping screws working on this principle are also known. In these, the part with the external thread (screw) also necessarily has to be machined especially. Only an angle of rotation of 60.degree. is available for the screwing movement, and therefore the longitudinal travel is restricted to only one sixth of the pitch of the thread. The two parts have to be in a specific angular position relative to one another in order to be joined together.
German Offenlegungsschrift 2,311,485 makes known a measuring device of snap gages, in which the objects to be measured are clamped in a special clamping block by means of a simple screw bolt. When the objects to be measured are changed, either the entire clamping block has to be exchanged, or if only the clamping width is different the screw bolt has to be rotated laboriously up to the appropriate clamping width. The result is a high outlay for the stock-keeping of the clamping blocks and long conversion times.